Ultra high frequency electronic device



A. E. BOWEN ULTRA-HIGH-FREQUENCY ELECTRONIC DEVICE Original Filed July 5, 1942 FIG. I

FIG. 4

FIG.- 3

INVENTOR A. E. BOWEN BY @W/ m A T TORNE Y Patented Oct. 14, 1947 "ULTR'A' HIGH FREQUENCY ELECTRONIC DEVICE aArnoldiE. 'iBowen, Red Bank, #N. tl -rassignor to Bell Telephone Laboratories, Incorporated,

New York, :N. -Y., aqcorporation-ofNew York *Origina'l -application July 3, 1942, Serial No. '449'581. 'Divided-and this-application-October .-9,1945, SerialNo. 621,366

-2 Olaims. 1

This invention relates to "systems employing resonators and :resonant Jcaviti'es soshaped and constructed as to be suitable f0l' reaction with an electron stream "to enable an electromagnetic field which .may be set upiin the resonator .or resonant cavity to induce :a variationin some characteristic property of the electron stream, or, to :permit an .'.interchange of energy between the resonator and the electronstream.

In'particular the resonator may belinthe shape oi-a short .sectionof an elliptical cylinder, hollow inside. and closed off-byparallelplane sheets. A waveguide maybe connected tothe resonator at a focal point or elsewhere according to the amount of impedancerto'be-provided at the junction point.

The invention is applicable generally to amplifiers, oscillators, modulators, detectorsand the like particularly at ultra-high frequencies, whereeverlit is desiredto effect direct interaction between an electromagnetic field and an electron stream.

This'application'is-a division of my copending applicationserial No. 449,581, -filed July 3, 1942, which application is in turn a continuation in part of my copending application SerialNo. 387,- 432,filed April 8, 1941,'Patent No. 2,408,409, issued October 1, 1946.

The'present application is specifically directed to an oscillator and harmonic-generator formed by an elliptical cavity resonator and a circular cavity resonator with electronic coupling between a focal point of the elliptical resonator and the ploying-anelliptical resonator and a circular resonator.

In Figs. 1 and 2 there are shown two substantially elliptical resonators 31 and 38 IWith focal points indicated at 39 and 40. The resonators may be built with walls of copper or other suitable material, the inner surfaces, at least, being preferably highly conductive. Each resonator may be viewed as comprising a short section of elliptical cylinder closed off by parallel, plane end walls. Apertures are cut through the plane wallsof each ellipseat' focus '3'9-and the-resonators are joined by a cylindrical conductive tube Al cove'ring'the apertures. Additional apertures are cut through the resonator iwalls preferably near the periphery at :apoint remote from focus-39 and the resonatorsare joined at'thls point by a cylindrical conductive tube 42. =CoaXially with. tube ilisplaceda rod of conductive materiall+3 which :is held in 11318.06 by insulating hermetic seals at M and 4-5. -A.-hollow conductive cylinder I6'is fastened-over an aperture-5 in the left-hand end wall of the resonator vEal as viewedin-Fig. 11. The tube 6 is joined by means ofa suitable -her-- metic seal 1 to an insulatingenvelope 8 of'glass or other suitable material. Within the envelope 8 are provided theusualel'ements of an electron gun .or beam projector 46 of any suitable type comprising, for example, a cathode 9, and :an accelerating electrode! cooperating withthe cylinderfi to directan electron beam through the apertures in the resonators =31 and :33 aligned with the axis of tube 4!. A pair of gaps 4-1 and 48 are constituted, as indicated, inthe path of the beam. The gap-G8 is'defined by the'edges of the aperture tliand the edges -of an aperture inthe right-hand end wall of the resonator -31 at the entrance of the tube' ll. The gap- 4 1 is defined by the'edges of anaperture in the lefthand end wall of the resonator 38 and-the right hand end wall ofthat resonator. Batteries ll, I 2 and Her other suitable sources may be :prm vided, respectively, for heating the cathode :9 energizing the accelerating electrode Ill and ap plying an accelerating potential to the conductive system 'comprisingthe. resonators '3"! and 38, and the tubes ll, 42 .alldifi. The tube 41 serves not only as a passage for the electron stream but also as an electromagnetic shield defining a drift space within which the electron bunching action hereinafter described'may be effectuated free from fluctuating electromagnetic fields.

In the operation of the arrangement of Figs. 1 and 2, the electrons comprising the electron stream from the gun lfi are'subjected at the gap 48 to interaction with any electromagnetic field which may exist in the resonators-l and at the gap 5'! with any such field that may exist intlie resonator "38. 'An accidental irregularity in the charge'density of the electron stream will suf= fice to set up an electromagnetic wave in the resonator 38 as the irregularity passes across the gap 41. The wave thus set up spreads through the cavity of the resonator 38 and converges again at the focus 4D, inducing current in the conductor 43 where the latter crosses the cavity. An

magnetic field in the resonator 31, depending-,

upon the phase of the field during its transit of the gap. The velocities of the electrons are varied in accordance with this energy interchange.

After leaving the gap 48, the velocity-varied electrons pass through the tube 4| where a group- 4 V sects an elliptical resonator 83. The'right-hand portion of the coaxial line beyond the resonator 83 is adjustable for tuning purposes by means of a piston 84 slidable over the conductor 8|. An electron gun represented schematically at 85 is arranged to send an electron stream across a gap '86 in the resonator 83, through a drift tube 81 and across a gap 88 to a collector 89. The gap 88 is situated at the center of a circular resonator 98. Theplan view is shown in Fig. 4.

In the operation of the system of Figs. 3 and 4 a wave to be amplified or to have its frequency multiplied is brought into the system through the ing or bunching effect takes place, those electrons which have lost energy and have, as a consequence, been slowed down being overtaken by 0th or electrons which entering later, have gained energy and have speeded up. Consequently, at a,

point some distance to the right of the gap 48, the electrons are traveling in more or less well-defined groups. Upon reaching the gap 41 the bunches of electrons may, if the length of the tube 4| and the initial speed of the electrons have been adjusted correctly, cross the gap 41 in opposition to the high frequency electromagnetic field, thus contributing energy to the field, and in greater amounts than are absorbed by the thinly distributed electrons which may cross the gap 41 during the unfavorable phase of the high frequency field. The net energy contributed by the electron stream to the field tends to sustain and build up the original wave and thus to maintain the system in oscillation.

It may be further noted that thewave above described, upon first arriving at the gap 48 and ithere initiating an electron group in the electron stream, is, in effect, reflected back through the resonator 31 and coaxial line 42, 43 into the resonator 38 and to the gap 41. If the velocity of the electrons in the beam is adjusted so that the electron bunch reaches the gap 41 at the same time the reflected Wave arrives there, or an integral number of cycles later, a fresh supply of energy is given to the wave and the oscillation is maintained. The adjustment in this case will also satisfy the condition for oscillation specified in the preceding paragraph.

The type of construction shown in Figs. 1 and 2 accommodates a magnetizing coil 49 which may be wound around the cylinder 4| and usedto improve the collimation and focusing of the electron stream. Energy may be extracted from the system by any suitable means, such as a coupling loop I98 connected across a coaxial transmission line |9|. The vacuum chamber will include the envelope 8, the resonators 31, 38 and the tubes 8, 4|, 42 and the closure may be completed with an insulating seal 92. The spent electrons are collected at the right-hand end wall of the resonator 38 and returned to the battery 3.

The construction shown in Fig. 1 will be obe served to require a minimum of insulating material and practically none in the space contain- 'ing the high frequency field. V

Figs. 3 and 4 show an application of the invention to an amplifier or a, frequency multiplier and also combine the use of electrical and circular resonators. An input coaxial line with in nor conductor 8| and outer conductor 82 intercoaxial line 8|, 82. The incoming wave sets up waves in the elliptical resonator 83 which Waves are focused upon the gap 86 where velocity variation of the electron stream from the electron gun is effected. After passing through the drift tube 81, the electron stream with its electrons bunched supplies energy at the gap 88 to set up an electromagneticfield in the circular resonator 98. The waves generated in the generator 98 may be of greater energy and hence amplified with respect to the waves supplied to theinput of the device. Theoretical considerations show that the electron stream crossing the output gap is characterized by a rather complex variation in space charge density which renders the stream capable of exciting 0501112..- tions of multiplied frequency in a properly designed resonator. .To take advantage of frequency multiplication the resonator 98 may be designed with sufiiciently small dimensions to resonate a desired harmonic of the input wave.

If amplification alone is desired .the resonator.

is preferably designed to resonate at the frequency of the wave impressed upon the system by the coaxial line 8|, 82.

The impedance presented to the line 8|, 82 by the resonator 83 is dependent upon the point of connectionof the line to the resonator. By proper selection of this point an impedance match may easily be secured. The point may be found by calculation or trial and will not, in general, be at the focus'of the ellipse.

What is claimed is: 7 V

1. An electronic amplifying device compris-v ing an elli tical cylindrical resonator and a circular cylindrical resonator spaced apart, an electron path providing a substantially unidirectional coupling between one of the focal points of said elliptical resonator and the center of said circular resonator, a coaxial transmission lineentering said elliptical resonator and means cou-- pled to said circular resonator for extractinguseful energy fromsaid circular resonator.

2. A harmonic generator comprising an ellipti-' cal resonator, a circular resonator spaced therefrom and resonant to a multiple of a resonant frequency of said elliptical resonator, conduit means connecting one of the foci of said ellipticalresonator with the center of said circular resonator to project an electron stream therethrough, means in said elliptical resonator to excite elec tromagnetic waves and means coupled to said circular resonatorto extract electromagnetic waves therefrom.

ARNOLD E. BOWEN. 

